1. Field of the Invention
The present invention relates to a novel process for the preparation of N-alkenylcarboxamides of the formula I ##STR4## where at least one of the radicals R.sup.1 is hydrogen, the second radical R.sup.1 is hydrogen or C.sub.1 -C.sub.4 -alkyl and R.sup.2 is hydrogen or an aliphatic, cycloaliphatic or aromatic radical.
The products of the formula I are desirable intermediates. N-Alkenylcarboxamides can be polymerized in a known manner and then converted by hydrolysis into the corresponding polyvinylamines. These polymers, in particular polyvinylformamine, are used, for example, for the preparation of dyes, pharmaceutical products, flocculants and viscosity standardizing agents in the paper industry (Linhard et al., Das Papier 46/10A (1992), p. V 38-45).
2. Description of the Related Art
N-Vinylformamide can be prepared by pyrolytic cleavage of ethylideneformamide at from about 300.degree. to 400.degree. C. Ethylideneformamide can be prepared, for example under mercury catalysis in acidic solution, from formamide and vinyl acetate (DE-A 40 36 097) or from formamide and acetaldehyde in the presence of acidic catalysts (U.S. Pat. No. 4,490,557).
Other methods of preparation are via intermediates such as N-acetylethylformamide (G. Parris, App. Cataly., 78 (1991) 65), N-alkoxyethylformamide (DE-A 3 622 013, DE-A 3 520 829 and U.S. Pat. No. 4,670,531), N-hydroxyethylformamide (U.S. Pat. No. 4,567,300) and N-cyanoethylformamide (DE-A 3 443 463). These compounds eliminate acetic acid, alcohols, water and hydrogen cyanide, respectively at relatively high temperatures of approximately 300.degree. to 400.degree. C.
The stated preparation processes are two-stage and require a thermal elimination step. They are thus technically relatively complicated and, owing to losses of end product at the required high reaction temperatures, give only unsatisfactory total yields. It is an object of the present invention to provide a process which avoids the stated disadvantages of known processes.